While not limiting, a particularly relevant application of the present invention is in the fabrication of a variety of electron emitting electrodes and gas-discharge plasma display systems which comprise cathode(s) and electrically excitable gas(es). Fabrication of plasma display systems requires that cathode material(s) which can emit electrons be caused to be present in desired patterns on substrates which are situated in close proximity to said electrically excitable gas(es). Preferably said cathode material(s) should have a low work function such that electrons can be easily emitted therefrom in use, and said electrically excitable gas(es) should be capable of providing desired, (eg. visible), electromagnetic wavelengths when electrical discharge is caused to occur therein by application of electric potential to closely situated cathodes.
Approaches to improving gas-discharge plasma displays include:
a. development and use of improved cathode material(s); PA1 b. development and practice of improved cathode material deposition; and PA1 c. development and use of improved electrically excitable gas(es). PA1 a. screen printing; PA1 b. plasma spray deposition; PA1 c. vacuum deposition by sputtering or evaporation; PA1 d. cluster-assisted deposition; PA1 e. light-induced deposition from solution. PA1 a. disolving B.sub.10 H.sub.14 and said GdCl.sub.3 in an organic solvent comprising methanol; PA1 b. providing and placing a substrate in said solution of B.sub.10 H.sub.14 and said GdCl.sub.3 in said organic solvent comprising methanol, so that a surface of said substrate is submerged, but accessible by electromagnetic radiation through said solution of B.sub.10 H.sub.14 and said GdCl.sub.3 in said organic solvent which includes at least one selection from the group consisting of: (methanol, THF, hexane, ether, benzene, nitrile and amine); PA1 c. providing a source of electromagnetic radiation and exposing the surface of said substrate to electromagnetic radiation through said solution of B.sub.10 H.sub.14 and said GdCl.sub.3 in said organic solvent comprising methanol, from said provided source of electromagnetic radiation;
While the development and use of improved electrically excitable gas(es) is a very viable and worthy approach to improving operation of gas discharge display systems, the present invention is focused on development and use of improved cathode material(s) and development and practice of improved cathode material(s) deposition onto substrates which can be adapted to comprise plasma discharge displays.
In view of the focus of the present invention, it is noted that various approaches to fabricating substrates which have cathode material(s) present thereon in desired patterns, have been investigated by previous researchers. Such techniques include:
The present invention was arrived at by experimentation in the area of light-induced deposition of cathode material(s) from solution, (preferably organic solvent based), and the present invention is found in practice of a method and the results of the practice thereof.
A search of Patents focused upon gas-discharge plasma displays provided a Patent to Kolwa et al., U.S. Pat. No. 5,159,238, which describes a gas discharge panel with a plurality of electrically conductive oxide cathode electrodes formed from, for instance, lanthanum, chromite, lanthanum calcium chromite, aluminum doped zinc oxide, or antimony-doped tin oxide.
Continuing, and of somewhat more relevance, a Patent to Lafferty, U.S. Pat. No. 2,639,399, and a Patent to Kauer, U.S. Pat. No., 3,399,321 disclose that rare-earth hexaborides have low work functions and are very suitable to application in electron emitter and filament applications. A Patent to Yokono et al., U.S. Pat. No. 4,599,076 describes production of a discharge display involving the cathode forming steps of applying a paste prepared by mixing LaB.sub.6 powder with alkali glass powder in proportion of 20-40% by weight to a base electrode, then burning the paste and then activating the paste by gas discharge with large current after an exhaustion step. A similar process leading to a similar result is also described in U.S. Pat. No. 4,600,397 to Kawakubo et al. A Patent to Kamegaya et al., U.S. Pat. No. 4,393,326 describes a gas discharge panel with an electrode comprised of a metal layer, (eg. Fe and Ni), and a metal compound layer, (eg. alkaline earth metal oxide or sulphide and rare-earth metal hexaboride), which are formed by a plasma spray technique. Another Patent which describes use of a rare-earth hexaboride such as LaB.sub.6 in forming cathodes in a plasma discharge display is U.S. Pat. No. 4,727,287 to Alda et al. Another Patent, U.S. Pat. No. 5,277,932 to Spencer, describes application of chemical vapor deposition techniques to deposit metal boride films onto substrates utilizing metal borane cluster compound as a precursor. While this method is successful, it does not lend itself well to either selective area depositions, or to depositions in large scale area manufacturing where substrates can have dimensions of several inches.
The above Patents show that the use of low work function rare-earth hexaborides to form cathodes in electron emitter, filament and gas plasma displays is not new, and that various techniques exist for forming such rare-earth containing cathodes. However, no known Patent describes the formation of rare-earth containing cathodes by a method comprising light-induced deposition (LISD) from solution. This is even more so where the solution is organic solvent based. It is noted that organic-based solvent based solutions, (eg. those containing methanol, nitriles or amides), as opposed to aqueous solutions, absorb wavelengths in the ultraviolet and are therefore often overlooked in the practice of light-induced deposition from solution.
Additional searching performed with an eye to identifying the application of light-induced deposition (LISD) from solution in formation of rare-earth containing electrodes provided very little. A Patent to Liepins, U.S. Pat. No. 4,464,416 describes a procedure which is purported to be applicable to forming a metallic coating on a polymeric substrate, comprising contacting the polymeric substrate with a fluid containing a metal compound at a temperature below 150 degrees centigrade for a time sufficient for the metal to be sorbed into the substrate, and then subjecting the substrate to a low pressure plasma. A perhaps somewhat more relevant Patent is U.S. Pat. No. 3,484,263 to Kushihashi et al. in which a process for forming a layer of semi-transparent gold on the surface of glass is described as comprising the steps of containing a water-soluable gold salt and a reducing agent in contact with said glass while subjecting said glass to short wave rays in the range of 250 to 500 Nanometers, with the improvement being that the solution is maintained at a temperature of not more than 10 degrees centigrade. Another Patent, U.S. Pat. No. 4,511,595 to Inoue, describes the deposition of a metal to a substrate from a typically flowing solution, wherein a laser beam is directed onto the substrate over a localized area, to activate an interface between said localized area and said solution. A Patent to Braren et al., U.S. Pat. No. 5,260,108 describes deposition of a metal such as palladium onto a substrate such as a polyimide, silicon dioxide, tantalum oxide or polyethylene terephthalate by contacting the substrate surface with a solution of the metal, and then exposing the surface of the substrate to laser radiation characterized by a wavelength absorbable by the substrate and a power density and fluence effective to release electrons to promote deposition of the metal onto the substrate without thermal activation of the substrate or the solution. Finally, a Patent to van der Putten et al., U.S. Pat. No. 5,059,449 describes depositing a nobel metal such as platinum from a salt solution thereof, onto a substrate which can be an insulator, semiconductor or conductor, by use of a laser beam. The solution is described as consisting essentially of a solvent selected from the group consisting of ammonia, a cyclohexanel and an amine, and typical metals which can be deposited are described as Pd, Pt, Rh, Ir, Ru and Ag. Application of the laser through masking to define areas of metal deposition is also described.
Articles of which the inventors are aware include:
A paper which describes the low work function of rare-earth metal borides is titled "Thermionic Emission Properties of LaB.sub.6 and CeB.sub.6 In Connection With Their Surface States, Examination By XPS, Auger Spectroscopy And The Kelvin Method", Berrada et al., Surface Science 72, 177 (1978).
Application of rare-earth metal borides in thermionic emitters is discussed in:
"Microcircuits By Electron Beam", Broers et., Sci. Am. 227, 34 (1972);
"Lanthanum Hexaboride Electron Emitter", Ahmed et al., J. App. Phys. 43, 2185 (1972);
"Electron Beam Fabrication", Miller et al., Solid State Technology, 16, 25 (July 1973);
"Evaluation of a LaB.sub.6 Cathode Electron Gun", Verhoeven et al., J. Phys. E, Scientific Instruments, Vol. 9 (1976);
"Field Emission Pattern Of LaB.sub.6 -Single Crystal Tip", Shimizu et al., J. App. Phys., Vol. 14, No. 7, 1089 (1975);
"Highly Stable Single-Crystal LaB.sub.6 Cathode For Conventional Electron Microprobe Instruments", Shimizu et al., J. Vac. Sci. Technol., 15(3), 922 (1978);
Articles which describe reaction of nido-decaborane and metal chlorides and subsequent chemical vapor deposition (CVD) of gadolinium hexaboride are:
"Chemical Vapor Deposition Of Metal Borides, 4: The Application Of Polyhedral Boron Vapor Deposition Formation Of Gadnolinium Boride Thin-Film Materials", Kher et al., Appl. Organ. Chem., Vol. 10, 197 (1996); and the previously cited Patent, U.S. Pat. No. 5,277,932 to Spencer also discusses this topic.
Similar rare-earth boride deposition, (where gadolinium was not the rare-earth involved), is discussed in:
"The Deposition Of Metallic And Non-Metallic Thin Films Through The Use Of Boron Clusters", Zhang, Kim, Dowben & Spencer, Chemical Perspectives of Microelectronic Materials III, Ed. by C. R. Abernathy et al., Mat. Res. Soc. Symp. Vol. 131, Proc. 282, 185 (1993);
"Metallized Plastics 4: Fundamentals and Applied Aspects", Ed. Mittal et al., Mercel Dekker Inc., New York (1997).
Selective area deposition of copper metal films from solution is described in:
"Laser-Induced Selective Copper Deposition On Polyimides And Semiconductors", Hwang, Kher, Spencer & Dowben, Mat. Res. Symp. Proc., Vol. 282 (1983);
"Material Deposition", Bauerle, Chemical Processing with Lasers", ED. Queisser, Springer Verlag (1986);
"Surface Processing Leading To Carbon Contamination Of Photochemically Deposited Copper Films:, Houle et al., J. Vac. Sci Technol., A 4(6) 2452 (November/December 1986);
"Photochemical Generation And Deposition Of Copper From A Gas Phase Precursor", Jones et al., Appl. Phys. Lett., 46, 97 (January 1985);
"Laser Chemical Vapor Deposition Of Copper", Houle et al., Appl. Phys. Lett., 46(2), 204 (January 1985);
"LCVD Of Copper: Deposition Rates And Deposit Shapes", Moylan et al., Appl. Phys. Lett. A 40, 1 (1986);
"High-Speed Laser Chemical Vapor Deposition Of Copper: A Search For Optimum Conditions", Markwalder et al., J. Appl. Phys., 65(6), 2470 (March 1989);
"Laser Enhanced Electroplating And Maskless Pattern Generation", von Gutfeld et al., Appl. Phys. Lett., 35(9) (1979);
"Laser-Enhanced Jet Plating: A Method Of High-Speed Maskless Patterning", von Gutfeld et al., Appl. Phys. Lett., 43(9), 876, (November 1983);
"High-Speed Electroplating Of Copper Using The Laser-Jet Technique", von Gutfeld et al., Appl. Phys. Lett. 46(10) (May 1985);
"Investigation Of Laser-Enhanced Electroplating Mechanisms", Puippe et al., J. Electrochem. Soc., Vol. 128, No. 12, 2539 (December 1981);
"Laser Induced Copper Plating", Al-Sufi et al., J. Appl. Phys. 54(6), 3629 (June 1983);
"Laser-Induced Decomposition Of Organometallic Compounds", Gerassimov et al., XII International Quantum Electronics Conference, (1982);
"Photoelectrochemical Deposition Of Microscopic Metal Film Patterns On Si and GaAs", Micheels et al., Appl. Phys. Lett., 39(5), 418 (September 1981).
Selective area deposition of complex compound material films from solution is described in:
"Structural And Electrical Properties Of Crystalline (1-x) Ta.sub.2 O.sub.5 - xAl.sub.2 O.sub.3 Thin Films Fabricated By Metalorganic Solution Deposition Technique"et al., Joshi et al., Appl. Phys. Lett. 71(10), 1341 (September 1997);
"Metalorganic Solution Deposition Technique", Joshi et al., Appl. Phys. Lett. 70(9), 1080 (March 1997).
A reference which describes a laser induced solution deposition process which involved copper chloride (Cu.sub.2 Cl.sub.2) and nido-decaborane is:
"Solution Deposition And Hetroepitaxial Crystalization Of LaNiO.sub.3 Electrodes For Integrated Ferroelectric Devices", Cho et al., Appl. Phys. Lett. 71(20), 3013 (November 1997);
It is noted that Laser Induced Solution Deposition (LISD) requirements (eg. transparent solvent/solute mixture and solid surface area which acts as a dipole that has a large dielectric response. An article which makes clear that similar requirements apply where selective area chemical vapor deposition is practiced is:
"Designing Of Organometallics For Vapor Phase Metallization Of Plastics", Boag & Dowben, Metallized Plastics 4: Fundamental and Applied Aspects, ED Mittal, Marcel Decker, New York (1997).
Deposition of electrode material (eg. LaNiO.sub.3) on substrates to which it does have a good lattice match is described in:
"Effect Of Textured LaNiO.sub.3 Electrode On The Fatigue Improvement Of Pb(Zr.sub.0.53 Ti.sub.0.47)O.sub.3 Thin Films", Chen et al., Appl. Phys. Lett. 68(10), 1430 (March 1996);
"Preparation of (100)-Oriented Metallic LaNiO.sub.3 Thin Films On Si Substrates By Radio Frequency Magnetron Sputtering For The Growth Of Textured Pb(Zr.sub.0.53 Ti.sub.0.47)O.sub.3 ", Yang et al., Appl. Phys. Lett. 66(20), 2643 (May 1995);
A reference which describes the results of metal deposition which is influenced by nucleation centers is:
"Deposition Of Thin Metal and Metal Silicide Films From The Decomposition Of Organometallic Compounds", Dowben et al., Mat. Sci. Eng. B2, 297 (1989).
A reference which describes vacuum reactor deposition of nickel boride is:
"Chemical Vapor Deposition Precursor Chemistry. 3. Formation And Characterization Of Crystalline Nickel Boride Thin Films From The Cluster-Assisted Deposition Of Polyhedral Borane Compounds", Kher et al., Chem. Mater., 4, 538 (1992);
A reference which describes fabrication of bulk gadolinium borides (an amorphous boron) as a result of thermolysis of a molecular precursor Gd.sub.2 (B.sub.10 H.sub.10).sub.3 is:
"Synthesis Of Cerium And Gadolinium Borides Using Boron Cage Compounds As A Boron Source", Itoh et al., Mat. Res. Bul. 22, 1259 (1987).
Even in view of the large number of references, there remains need for additional, simple and efficient, techniques for selective area laser induced deposition of rare-earth borides onto substrates.